Mammoth or pigeon? De-extinction's choices
The art and science of resurrection
Imagine that you are standing on the streets of Toronto or Hamilton on a spring day sometime in the 19th century. The skies begin to darken as a massive flock of birds passes overhead, blotting the sun. The beating of billions of wings rumbles like thunder, stirring up a wind that chills you to the bone. The flock might take days to pass. The birds were passenger pigeons, once found across North America east of the Rockies. About the size of our pigeons today, the males had a coppery breast, the females were somewhat plainer, and they travelled in gargantuan numbers. A single flock could stretch over 150 kilometres, and number in the billions: in the spring of 1860, a flock estimated at over 3.7 billion birds flew over Ontario. Gorging themselves on tree nuts, such as acorns, they could clear entire forests; the weight of roosting pigeons would cause whole limbs to drop from the trees. And we think pigeons today are a pest.
Passenger pigeons were once the most abundant bird in North America, maybe in the world. At one point, they outnumbered humans on our planet. But over the course of just 50 years, we managed to wipe them out, hunting them to oblivion. (Martha, the last of her kind, died in 1914 at the Cincinnati Zoo.) Until very recently, the extinction of the passenger pigeon—a plump, tasty creature once served in restaurants in New York and Toronto—seemed a shame, and simply that. Some now see it as an opportunity. New technologies could allow us to bring the passenger pigeon back from the dead—to “de-extinct” it, in the somewhat clunky terminology of the day. It is just one candidate species that has been floated for conjuring from the past, alongside the Neanderthal, the T. rex, and the fan favourite, the woolly mammoth. If a variety of pigeon seems a humble animal to resurrect, there are other conservative choices, including a strange little frog that vomits its babies out of its mouth when it reproduces, and which went extinct in the 1980s.
In her new book, Rise of the Necrofauna: The Science, Ethics, and Risks of De-Extinction, Britt Wray, a Canadian biologist turned science writer who is now based in Copenhagen, examines many such candidates for de-extinction, as well as the thorny ethics and risks of this new and rapidly advancing field. To return to the example of the passenger pigeon, if scientists do manage to bring it back in sufficient numbers and re-release it into the wild, would it reclaim its place within the ecosystem and help restore balance in our forests? Or would it blot the skies, rain sheets of feces over our cities, crowd out other animals, spread disease, and generally make a menace of itself? Would we drive it into extinction all over again? These are important questions that have been explored in a glut of recent articles, documentaries, and books—Helen Pilcher’s Bring Back the King: The New Science of De-Extinction is another recent long-form examination of the subject.
Given the hold that de-extinction seems to have on our collective imagination and the outsized coverage the subject receives, it’s worth emphasizing that only a handful of researchers around the world are seriously attempting this. It’s all still science fiction. (Early in her book, Wray describes de-extinction activities as “fringe.”) Even so, it is easy to understand the fascination. Aside from a scientific story that borders on the fantastical, there is a wonderfully optimistic cultural narrative here. While the loss of the passenger pigeon is tragic, that species is not unique. Rates of extinction are speeding up on our planet, and human activity is largely to blame. Now along comes the promise of new technology that can get us out of this jam. It’s little wonder, then, that de-extinction is a more gripping subject than how to curb ocean acidification or stop plastic pollution.
On January 6, 2000, a wild mountain goat named Celia was found crushed to death by a falling tree branch in the Spanish Pyrenees. Celia happened to be the last living bucardo (or Pyrenean ibex) and her death signalled the extinction of the subspecies. But before she died, a prescient veterinarian named Alberto Fernández-Arias froze some cells from her ear in liquid nitrogen, a technique called cryopreservation. “This kept Celia’s cells whole and intact,” Wray writes. “Exactly what is needed for cloning.”
Scientists took nuclear DNA from Celia’s cells and put it into goat eggs stripped of their own genetic material. These goat eggs, filled with extinct bucardo DNA, were then implanted into surrogate mother goats. Wray notes that it took more than 200 implantation attempts in 57 goats to get seven of them pregnant. Only one was brought to term. And so, on July 30, 2003, what Wray calls “the world’s first un-extinct animal” was born—Celia’s clone. The animal died ten minutes later, its lungs terribly deformed. The bucardo disappeared, all over again.
Celia’s story shows that de-extinction will be a messy, complicated task—and that is just creating the creature, never mind reintroducing it into the environment. Cloning, which was the mechanism at work here, is one of several techniques being explored. It’s the same kind of experiment that produced Dolly the sheep in 1996, Pilcher writes in her own telling of the bucardo event. (The first mammal cloned from an adult cell, Dolly is the most famous sheep in the world.) But why stop at sheep, or even the bucardo? The renowned geneticist George Church, a major figure in the de-extinction movement, has argued for bringing back a Neanderthal. Wray quotes this excerpt from his book, Regenesis: “If society becomes comfortable with cloning and sees value in true human diversity, then the whole Neanderthal creature itself could be cloned by a surrogate mother chimp—or by an extremely adventurous female human.” (Church later said he was being taken too seriously.)
Another technique is selective breeding. This has been used to try and bring back the South African quagga, a subspecies of the plains zebra, which died out in the 19th century. By breeding zebras that resemble quaggas, Wray notes, you can get something close to a quagga. Gene editing is yet another possibility. Within the past decade or so, a genetic editing tool called CRISPR, which is remarkably powerful and easy to use, has been embraced by labs around the world. Scientists are experimenting with CRISPR to cure genetic disease, to make more productive crops, and for other surprising purposes: in 2015, a team in China reported using CRISPR to make extremely muscular beagles. CRISPR is being used in projects to revive both the passenger pigeon and woolly mammoth (more on that later).
None of these methods, though, can truly bring back an extinct creature as it once was—selectively bred plains zebras that look a whole lot like a quagga are not, to be completely accurate, a quagga. Nor was Celia’s clone a true bucardo: it was born of an egg from another type of goat, and grew to term in a non-bucardo mom, who would also likely have raised and socialized the clone, had it lived for more than ten minutes. As both Wray and Pilcher acknowledge, we need to abandon the idea that scientists will resurrect long-lost creatures in their “pure,” ancient forms. What they are attempting to create are genetically modified animals that are entirely modern and entirely new.
If a potent mix of nostalgia and techno-utopianism is a major driving force behind de-extinction—the title of Pilcher’s book, Bring Back the King, really sums it up—a deeper look into the details reminds us that very little about the work itself is truly nostalgic. It’s more about the future, or possible futures, which are allowed by technologies we possess today. The journey, and the choices it will entail, may be as exotic as the result, if not more.
On to the candidate species. The current scientific reality rules out dinosaurs—as do basic ethics; scientists in favour of de-extinction say we should focus on creatures that have an ecological niche to fill, and that can ideally be released into the wild. While Pilcher gamely devotes a chapter to dino resurrection, I can put that idea to bed right here: we won’t be seeing any Jurassic Park-style T. rexes in our lifetimes. Any dinosaur DNA that’s been left lying around for millions of years is simply too old, and too decayed, Pilcher explains.
Which may bring us back to our more pedestrian candidate. Ben Novak, a charismatic young scientist at the University of California at Santa Cruz, is leading the effort to resurrect the passenger pigeon. There may be good reason for bringing some extinct creatures back to life, even if in a new, modified form. Monster flocks of these birds once acted as a “super-organism,” he tells Wray, and profoundly shaped their environments. They would feast on nuts, seeds, and berries, then fly long distances, transporting those nutrients along with them. Some argue the disturbing effects of these birds’ behaviours on the ecosystem was akin to a forest fire, and spurred cycles of regeneration.
For better or worse, there are no cryopreserved passenger pigeon cells waiting in somebody’s freezer. Novak has been relying on stuffed and dried museum birds to obtain passenger pigeon DNA—including specimens from the Royal Ontario Museum, in Toronto, which has the largest collection in the world. This isn’t as good as a living cell, so in order to fill in missing gaps in the passenger pigeons’ DNA, Novak is consulting the genome of a close living relative, the band-tailed pigeon. Using CRISPR, he will edit passenger pigeon genes into band-tailed pigeon cells, Pilcher explains. There are still plenty of hurdles to clear. Cloning birds is exceedingly difficult, for one, so Novak is developing a workaround.
“Despite the hurdles, let’s say it all works,” Wray writes, and a baby passenger pigeon, or something like it, is born. How do we make it look and act like a true passenger pigeon, instead of the band-tailed pigeon? How do we prepare it to re-enter the environment, to train it to fly in massive flocks as it once did? How do we ensure it doesn’t become a “frightening pest,” as Wray says, that swarms above our cities in the billions? These birds evolved to travel en masse—we can’t just create a dozen and call it a day. Pilcher agrees: “We either bring back a flock so large it would darken the sky, or we don’t bother at all.”
While Novak presses on, another team, calling itself the Lazarus Project, is trying to resurrect the southern gastric-brooding frog. Working in their favour is the fact that, unlike cloning birds, cloning frogs has a healthy precedent. Pilcher writes that this frog, first described in Australia in 1973, was declared extinct a decade later. It had an unusual ability: the female hatched eggs inside her stomach, then belched up fully formed froglets.
Nobody had much of a chance to methodically study this animal before it vanished, and understanding its reproductive trick could lead to new therapies for stomach ulcers, for example. Yet there are major problems here, too: the frog is believed to have gone extinct because of a deadly fungus that humans introduced into its range. That fungus still exists today. It’s a good reminder that, even if we do succeed in pulling an animal out of extinction, we humans still haven’t reckoned with how to stamp the extinction impulse out of ourselves.
For supporters of the idea of de-extinction, the question of utility is never far from view. Standing face-to-face with a woolly mammoth, say, a creature that largely died out some 10,000 years ago, would be an undeniably stunning, possibly mind-altering experience. In her book, Wray considers whether we should bring back this—or any—animal simply because it would be “cool.”
Advocates make other persuasive arguments. They point out, for instance, that the woolly mammoth could possibly help prevent some effects of climate change, which is melting the Arctic permafrost where it once roamed.
In a remote corner of northeastern Siberia is Pleistocene Park, the creation of Russian scientist Sergey Zimov, and a well-trodden pilgrimage site for science journalists covering the de-extinction movement. Wray calls it a “rewilding experiment” that aims to return the landscape to what it may have looked like 10,000 years ago. Zimov has brought in large herbivores like Yakutian horses, reindeer, and moose, with local carnivores including wolverines and bears—animals thought to have once lived there.
Zimov’s work is driven by the idea that the ecosystems of Siberia were sent off-kilter by the loss of large mammals, near the end of the last Ice Age. The grasses that thrived here during the Pleistocene “reflected light from the sun but did not absorb much heat,” Wray explains. As large animals trundled around, they trampled darker, light-absorbing plants, and punched holes in the snow with their big, heavy feet. That snow provides insulation, and so by pushing it down, ancient megafauna cooled the Earth, circulating cold air below. The disappearance of these animals gradually converted what was once a sweeping grassland into tundra. Zimov believes that, by restoring the ecosystem, he could slow the melt of the permafrost—a subsurface layer of soil that stays frozen all year, and is now rapidly thawing because of climate change, releasing greenhouse gases. Permafrost melt is causing problems for communities in the North, including across Canada’s Arctic, destabilizing buildings and roads in communities like Inuvik and Tuktoyaktuk.
Church’s team at Harvard University is working to create a mammoth by using CRISPR to edit mammoth genes into an elephant cell, which will eventually be inserted into an elephant egg. If all goes according to plan, it will be carried to term by a mother elephant, producing a mammoth-elephant hybrid. (Pilcher writes that Church pictures it having “ginger” hair.) They have their challenges set out for them, including whether the mother elephant will be able to socialize the infant. (Pilcher believes the woolly mammoth isn’t an optimal candidate for de-extinction because it would involve “experimentation and invasive procedures” on its endangered living relative, the Asian elephant.)
Wray rightly emphasizes how distant these goals are for now. “When people hear about it, I think they get confused on the timescale,” Bobby Dhadwar, a postdoc in Church’s lab, tells her. “It’s not like we are anywhere close to giving birth to a woolly mammoth.” For now, the team is simply taking genes that have been identified in the woolly mammoth genome and introducing them into elephant cells, to see what happens next. If, one day, they do succeed—and for now that remains a big “if”—Church has expressed interest in sending mammoth-elephant hybrids to Pleistocene Park.
Which is, for me, where the de-extinctionists’ argument starts to fall apart. The climate is changing rapidly, nowhere more so than in the Arctic, a phenomenon known as polar amplification. It is wishful thinking that a bunch of hairy mammoth-elephant hybrids kicking holes in the snow could cool things down quickly enough to make a difference. Beyond that, there’s the question of moral hazard, which concerns both Pilcher and Wray: If the public believes we can bring extinct creatures back, will they be less invested in traditional conservation efforts? Most importantly, should we not focus on saving the species that are here now, today, and still have a fighting chance?
In a paper published in Nature Ecology & Evolution in 2017, Carleton University assistant professor Joseph Bennett and his co-authors examined “the merits of de-extinction as a biodiversity conservation tool.” They concluded it would cost in the millions to create and maintain a resurrected species, which would put such a strain on conservation budgets, it would threaten existing species. As Bennett said at the time: “It’s better to spend the money on the living than the dead.”
Perhaps this is why, of the two books, Pilcher’s appealed to me more. A former reporter for Nature with a PhD in cell biology and a background in stand-up comedy, Pilcher, who lives in rural Warwickshire, England, doesn’t mind having fun with a topic that—let’s admit—takes itself too seriously at times. (An admitted Elvis Presley fan, Pilcher devotes an entire chapter to whether we could resurrect the King himself, which turns into a fascinating discussion of human genetics, twin studies, and the many factors that make an individual unique.)
Wray approaches the topic with greater earnestness, although she has her moments. Describing her encounter with Dhadwar, the mammoth researcher, she writes that he “seems irked when I ask him what their artificial womb might look like.” Dhadwar reminds her that all they’re doing is twiddling with some genes. Even the title of Wray’s book—Rise of the Necrofauna—heralds a grandiose, slightly terrifying future that I’m not convinced is the one we are credibly headed towards.
Wray and Pilcher do find common ground arguing that conservation and de-extinction can exist side-by-side—that one need not steal resources and attention from the other. What this sort of de-extinction could look like, and achieve, is laid out most convincingly by Pilcher. The northern white rhinoceros, she explains, is not yet extinct but may as well be; there are three left on the planet: Fatu and Najin (both female), and Sudan (an elderly male). All live under heavy guard in Kenya. “There is no possible way the animals can breed themselves out of trouble,” Pilcher writes. “They’re too old, too ill and too related.”
Yet these rhinos matter—not only because they’re beautiful and iconic, but because they are “ecosystem engineers,” like passenger pigeons or woolly mammoths before them, and shape their environments as they graze on the grasslands of the savannah. So why not de-extinct the northern white rhinoceros before it’s actually gone extinct?
Pilcher suggests that the stockpiled cryopreserved skin cells of other northern white rhinos could be engineered to create embryos that would then be transferred to a surrogate’s womb—a close female relative, the southern white rhinoceros. In this way, one could imagine that Fatu, the youngest northern white rhino left, might live to see another of her kind.
It’s exciting to dream of woolly mammoths and copper-chested passenger pigeons thriving on our planet once again. “In the time it’s taken me to write this book,” Pilcher notes, “at least 20,000 species have gone extinct.” Many scientists agree we are living through the Earth’s sixth mass extinction period, with species disappearing at a terrifying rate. Ideally, technology can augment the traditional goals of conservation. But a blind faith in technology should not replace them.